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Old Tuesday 12th December 2006, 19:48   #1
henry link
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Zoom Eyepiece Test: Baader, Zeiss, Swarovski, Nikon

I recently acquired a new Baader Hyperion zoom eyepiece (24mm-8mm). This eyepiece comes with a 1.25" barrel and can also be attached directly to the Zeiss Diascope and Celestron/Synta spotting scopes. What is most interesting about the Baader is that it has, for a zoom, an unusually wide field at the low end of its magnification range, comparable to the Zeiss Diascope zoom. In the US it is available from Alpine Astronomical at a cost of $189. This is less than half the price of the Zeiss zoom eyepiece which could make it interesting to those thinking of purchasing a Diascope. I already own the Zeiss zoom (25.1mm-8.4mm), current Swarovski zoom (23.1mm-7.7mm) and Nikon 20x-60x MC zoom, NOT the MC II (21mm-7mm). All of these are adapted for use on astronomical telescopes. I tested all the eyepieces on an Astro-Physics 92mm f/6.6 APO refractor.

First let me dispense with the question of sharpness at the center of the field. On my AP refractor all of the eyepieces here are perfectly sharp in the center throughout their zoom ranges, just as sharp as fixed magnification eyepieces of very high quality. The birding scopes these eyepieces are used on will virtually always be the limiting factor for center sharpness.

There are performance differences, but they are in the areas of light transmission, contrast, color accuracy, eye relief, field width and off-axis field curvature, astigmatism, distortion and lateral color.

I measured the eye relief and apparent field of each eyepiece at four magnifications on the eyepiece barrel; 20x, 30x, 40x and 60x. I measured the Baader at 24mm, 8mm and two settings in between that would correspond to about 30x and 40x if it were mounted on the Zeiss Diascope. The Baader has “clickstops” which are supposed to correspond to 20mm, 16mm and 12mm. These are ridiculously inaccurate. The 20mm setting actually corresponds to about 13mm, the 16mm corresponds to 10-11mm and the 12mm corresponds to about 9mm. The end stops do seem to be close to 24mm and 8mm.

First the figures for eye relief. These are measured from the eyecup rim set at its lowest position. Distance to the glass of the eyelens would be longer by 4-5mm and with most of these eyepieces (except the Nikon) the eyecups are so wide that the center of a curved eyeglass lens will probably get closer to the eyelens than the rim of the eyecup, adding a couple of mm’s to the effective eye relief. These figures may look short, but I find I can see the entire field at every magnification with all the eyepieces while wearing reading glasses. Only the Nikon’s eye relief “feels” a bit short to me without glasses. All of the eyepieces show the usual dip in the middle of the zoom range.

Swaro 20x-16mm, 30x-12mm, 40x-10mm, 60x-14mm

Nikon 20x-12mm, 30x-8mm, 40x-8mm, 60x-12mm

Zeiss 20x-12mm, 30x-10mm, 40x-8mm, 60x-12mm

Baader 20x-11mm, 30x-9mm, 40x-9mm, 60x-12mm

Now the apparent field widths in degrees:

Swaro 20x-40, 30x-52, 40x-58, 60x-68

Nikon 20x-40, 30x-45, 40x-52, 60x-59

Zeiss 20x-50, 30x-57, 40x-62, 60x-71

Baader 24mm-49, 30x(16.8mm)-56, 40x(12.6mm)-60, 8mm-72

The Baader does have approximately the same apparent field as the Zeiss over its range. Both have wider fields than the the Swaro at low magnifications, but the gap narrows as magnification increases. The Nikon is just not very competitive when it comes to field width.

The clear loser in this group when it comes to light transmission, contrast and color accuracy is the Zeiss, which, compared to the others, is obviously dimmer and lower contrast with a yellow color cast. The Nikon, Baader and Swaro all have very high light transmission and contrast. About as good as it gets for complex eyepieces. The Baader is quite outstanding, possibly the brightest by a hair. It’s easily as bright or brighter than my Pentax 14mm XW and 13mm Nagler, and it gives up almost nothing in brightness and contrast compared to my 16mm Zeiss A-16 Ortho. Color transmission is also very accurate. The Baader and Nikon are nearly indistinguishable with very slight red casts and the Swaro is a tiny bit yellow, not blue like many people report for the complete Swaro scope optics.

There are some interesting differences in off-axis behaviour. Some of this, like distortion, will be exactly the same in other scopes, but field curvature and lateral color in other scopes may be different from my experience.

None of the eyepieces show significant off-axis astigmatism on the AP scope. Edge softness is almost entirely field curvature. At the lowest magnification the Baader has slightly less field curvature than the Zeiss. As magnification is increased field curvature decreases for both until they are about equal with very little curvature at 40x (12-13mm) and beyond. For comparison purposes this is an easy thing to measure by focusing an object at the edge, then moving it to the center and refocus, noting how much the focuser has to be rotated for different eyepieces. I’ve followed the recent discussion about how the Zeiss edge performance compares the the Swaro at low magnification so I also checked the field curvature of the Zeiss and Baader set at their lowest magnification at about 20 degrees off-axis and compared that to the Swaro set at 20x. The Swaro has a very flat field with very little astigmatism or field curvature all the way to the edge of its 40 degree field. Neither the Zeiss nor the Baader is quite as good at the edge of a 40 degree field circle. Their comparable “sweet spot” is about 30 degrees wide. The Nikon is close to the Swaro at low magnification but with a little more astigmatism. At short focal lengths the Baader and Swaro become excellent wide field, long eye relief eyepieces. The Zeiss is nearly as good except for the lower light transmission and contrast.

Distortion varies. There is mild barrel distortion at all focal lengths in the Swaro. The Nikon has very mild pincushion distortion at all focal lengths. There is moderate pincushion in the wider fields of the Zeiss and Baader which increases with magnification as the apparent fields get wider.The Baader has a bit more than the Zeiss, but neither has as much as, for instance, the TeleVue Panoptics at the same apparent field width.

I didn’t see any significant differences in lateral color in my telescope. It’s similar in all the eyepieces at the same distance from the center of the field. There is, of course, more at the field edges at high magnification as the apparent fields widen. I didn’t consider it to be a problem, but it could be worse in faster telescopes.

I haven’t had a chance to try the Baader on the Diascope yet, but it certainly looks like a real alternative. I prefer it to the Zeiss on my AP scope. On the Diascope it would produce a little more magnification than the Zeiss zoom (21x-63x on the 85mm), but would not be waterproof. Optically, I think the Baader is the best zoom eyepiece I’ve tried so far. It manages to combine the wide field width of the Zeiss with the high light transmission, contrast and color accuracy of the Swaro and Nikon, and at a bargain price. I can’t find much to complain about.

Too bad there isn't a Nikon adapter. I think the Baader would probably fit and the Fieldscopes would really benefit from this eyepece.

Last edited by henry link : Wednesday 13th December 2006 at 16:05.
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Old Wednesday 13th December 2006, 04:42   #2
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Quote:
Originally Posted by henry link
I recently aquired a new Baader Hyperion zoom eyepiece (24mm-8mm). This eyepiece comes with a 1.25" barrel.
I already own the Zeiss zoom (25.1mm-8.4mm), current Swarovski zoom (23.1mm-7.7mm) and Nikon 20x-60x MC zoom, NOT the MC II (21mm-7mm). All of these are adapted for use on astronomical telescopes. I tested all the eyepieces on an Astro-Physics 92mm f/6.6 APO refractor.

There are performance differences, but they are in the areas of light transmission, contrast, color accuracy, eye relief, field width and off-axis field curvature, astigmatism, distortion and lateral color.


First the figures for eye relief. These are measured from the eyecup rim set at its lowest position.
Swaro 20x-16mm, 30x-12mm, 40x-10mm, 60x-14mm

Nikon 20x-12mm, 30x-8mm, 40x-8mm, 60x-12mm

Zeiss 20x-12mm, 30x-10mm, 40x-8mm, 60x-12mm

Baader 20x-11mm, 30x-9mm, 40x-9mm, 60x-12mm

Now the apparent field widths in degrees:

Swaro 20x-40, 30x-52, 40x-58, 60x-68

Nikon 20x-40, 30x-45, 40x-52, 60x-59

Zeiss 20x-50, 30x-57, 40x-62, 60x-71

Baader 24mm-49, 30x(16.8mm)-56, 40x(12.6mm)-60, 8mm-72

Too bad there isn't a Nikon adapter. I think the Baader would probably fit and the Fieldscopes would really benefit from this eyepece.
Henry,

Outstanding review, very nicely thought out in a sequential manner. I have a question. I have a Swarvoski 80hd with a 20-60 zoom. I would like to get a stronger eyepiece mainly for the reasons, one to see the eye of a distant bird of prey and secondly for those few times I might use it for astronomy. I have been considering the Televue Nagler 7mm Type 6 and now you mention this Baader eyepiece. In your humble opinion what do you think is a nice addition to this one eyepiece I have now?

Last edited by greg g : Wednesday 13th December 2006 at 11:25.
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Old Wednesday 13th December 2006, 07:31   #3
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Henry,

Thanks for a most welcome and excellent review. I'll get back to commenting it (positively) in more detail as time permits.

What prompted me to respond quickly is the two responses to it. Could people please refrain from quoting an entire post in their replies unless that is absolutely necessary in light of what they are saying in response. Unnecessary quotes make reading a thread rather tedious. If you want to say something brief and do not need to quote, using the "quick reply" function works well and you don't have to delete any unwanted quotes.

Kimmo
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Old Wednesday 13th December 2006, 09:05   #4
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Thanks Henry for taking the time to do this excellent review of this eyepiece.Makes me want to run out and buy one.
Thanks Kimmo for the heads up about the quick post.
Regards,Steve

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Old Wednesday 13th December 2006, 09:27   #5
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Henry,
Thanks for the data! After seeing the ER values, I know why I never fell in love with zooms.
John
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Old Wednesday 13th December 2006, 11:27   #6
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Kimmo,

Thanks for the heads up on the quick reply, didn't realize that was an option.
Greg
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Old Wednesday 13th December 2006, 15:56   #7
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Quote:
Originally Posted by greg g
Henry,

Outstanding review, very nicely thought out in a sequential manner. I have a question. I have a Swarvoski 80hd with a 20-60 zoom. I would like to get a stronger eyepiece mainly for the reasons, one to see the eye of a distant bird of prey and secondly for those few times I might use it for astronomy. I have been considering the Televue Nagler 7mm Type 6 and now you mention this Baader eyepiece. In your humble opinion what do you think is a nice addition to this one eyepiece I have now?
Greg,

Thanks! The problem I see with the 7mm Nagler is that it will produce only 66x on the Swaro, not much more than the zoom which is itself an excellent wide field eyepiece at 60x with better eye relief than the Nagler. The Baader zoom might work on the Swarovski if it will reach focus, but the magnification range would be about 19x-58x. I'm using a 5mm Burgess Optical/TMB Planetary for maximum birding magnification. On your scope 5mm would produce about 92x. It's a very nice eyepiece and would allow you to see the smallest details your scope can show you, if it will reach focus, and it's cheap, $99.

Henry

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Old Thursday 14th December 2006, 05:28   #8
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I'm using a 5mm Burgess Optical/TMB Planetary for maximum birding magnification. On your scope 5mm would produce about 92x. It's a very nice eyepiece and would allow you to see the smallest details your scope can show you, if it will reach focus.


Henry,

Thank you for the reply, I will look into the 5mm Burgess Optical/TMB Planetary. The 92x I can only imagine would be incredible! On a previous thread I seem to recall it was mentioned that the power of an eyepiece (92x) should not exceed the size of the scope (80x), your Astro-Physics is a 92x. I don't know if this is true, what do you think of that?
If that is true should I then consider a 6mm Burgess Optical/TMB Planetary for a 80x scope? Is that what you meant about "if it will reach focus"?
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Old Thursday 14th December 2006, 07:57   #9
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Henry,

I'll offer just a couple of comments on the Nikon zoom. As you stated, your review sample is the first incarnation (MC) of the Nikon 21-7mm zoom. Since I have compared the MC and MC II versions against each other and have rather substantial experience with both, I thought I could add a bit by summarizing my findings.

Optically, the changes between the two are rather small. However, the new model has slightly better light transmission and just barely perceptibly better contrast. Fields of view are, unfortunately, identical at both extremes of the zooms' range, but at 14mm, I measured the new zoom's field as about 2% wider. I measured the fields only at 7, 14 and 21mm since the results at these focal lengths were so near to identical there seemed no point to spot check further. I measured eye-reliefs at the same settings. Since both zooms have the same eyelens diameter, the expected outcome was that there was no E-R difference at the extremes, but at 14mm the new zoom had very little bit less.

A more obvious difference I found in off-axis performance. Using the USAF chart, at 21mm the new zoom could resolve two more elements at the edge of the field, at 14mm five more elements and at 7mm one to two more elements. The new zoom is thus markedly better corrected for off-axis astigmatism and field curvature. I no longer have the earlier version of the zoom and my notes make no reference to barrel or pincushion distortion differences between them.

The only additional note I have is that the first version of the zoom gave a rather prominent yellow-green "frame" to the image at the lowest zoom settings, and this is virtually gone from the MC II.

Physically, they are a little different. The MC II was designed to accept Nikon's own digiscoping adapters, and therefore threads in directly into the scope body whereas the MC had a threaded locking ring on the eyepiece body that allowed one to fasten the eyepiece in any rotational alignment so that you could have the zoom scale markings visible on any side you chose. The MC II has a much narrower zoom adjustment ring, and if my memory serves me right, is also a bit stiffer to zoom.

I'm grateful that the Baader zoom gave you the inspiration to write up this zoom eyepiece review. I will file it among my reference articles.

Kimmo
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Old Thursday 14th December 2006, 14:00   #10
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Kimmo,

Thanks for you additions. I'm sorry I didn't have an MC II available since that is the only one that can be purchased now. I was surprised to read about the improvements in off-axis performance, which I think is already pretty good in the MC. Your mention of using a bar target at the edge made me realize that I had been a bit too casual in evaluating edge performance. I used the USAF 1951 target, but was lazy about recording measurements, so I think my descriptions are too vague. I compared the eyepieces again, this time recording edge measurements and found some differences from my original descriptions worth reporting, so here I hope is a better description of edge performance in the AP scope.

Firstly, all the eyepieces have a bit more astigmatism than I reported. At some focal lengths it is significant. At the lowest magnification the Swaro still looks the best at the edge of its 40 degree field. There is only a loss of about 1 element on the chart which is only about a 12% drop in visible detail compared to the center. The Nikon looses 2 elements which is still quite good. The loss at the edge of the Baader's 49 degree is naturally worse, a loss of 4 elements, about 50-60%, mostly from field curvature. The Zeiss is considerably worse with a loss of 8 elements, about half from field curvature, the rest from astigmatism. What that means is that if 4 arc second details are visible at the center, then the Baader will show about 6 arc second details at the edge while the Zeiss will show details no smaller than about 12 arc seconds. Of course no one looks at details at the edge, but this is the only way i know to quantify the differences. At the edge of a 40 degree field circle (same as the total field width of the Swaro and Nikon) the Baader improves to nearly equal the Swaro with a loss of only one element, while the Zeiss improves to a loss of 3 elements.

At the highest magnifications all the eyepieces have much wider apparent fields so these results cannot be directly compared to the low magnification results. At the highest magnification the Zeiss is a bit better than the Baader, showing a loss of 5 elements at the edge of a 70 degree field compared to a loss of 7 elements at the edge of a 72 degree field, in both cases astigmatism accounts for about a 2 element loss and the rest is field curvature. The Swaro loses about 4 elements at 68 degrees and the Nikon MC about about 6 elements at 58 degrees. An MC II should do about 2 elements better. In the Swaro and Nikon astigmatism dominates, accounting for 3 elements in the Swaro and about 5 elements in the Nikon MC. To see how these results compare to a premium quality fixed magnification eyepiece I tested a Pentax 14mm XW. It showed a loss of about 5 elements at the edge of a 70 degree field, almost all from field curvature, quite similar to the Zeiss.

I should caution that these results were obtained in a well corrected f/6.6 telescope. Off-axis performance in other telescopes will not be quite the same. It should be better in high focal ratio scopes and probably, but not certainly, worse in faster scopes. Another unpredictable variable is vignetting. The AP scope is designed to completely avoid vignetting with even the widest field, long focal length eyepieces. It's surprising how many astronomical refractors show some partial vignetting from the focusing tube or some badly placed tube baffle and spotting scopes are often worse because of undersized erecting prisms. Most of the other characteristics I tested for should still be true for other scopes, but off-axis performance (except distortion) is less predictable.

Henry

Last edited by henry link : Thursday 14th December 2006 at 15:27.
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Old Thursday 14th December 2006, 21:28   #11
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Henry once again what a great job.Having done some of this edge performance using the USAF 1951 test target on binoculars I know it takes some time to do this..Thanks a lot for your time and all this information.Did you notice much difference between the Zooms as far as center field resolution?Thanks again.
Regards,Steve

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Old Thursday 14th December 2006, 22:20   #12
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Diascope at high power.

[quote=greg g] I would like to get a stronger eyepiece mainly for the reasons, one to see the eye of a distant bird of prey and secondly for those few times I might use it for astronomy. QUOTE]

I've been using a Meade 5000 4.7mm eyepiece ($200) on a Diascope 85 yielding 107x and it provides very nice, 82 degree apparent field, views. The optics of the Diascope stand up very well at this power. Of course the view starts getting dimmer, especially in anything other than bright sunlight. I've used this combo for some casual astro observing and find that it works beautfully on the Moon, planets, star clusters, double stars, the Sun (with appropriate objective end solar filter), etc.. Although I've looked at the moon through all kinds of scopes including 12"+ scopes, the first view of it with this combination nearly knocked my sox off. It's a huge, very bright, and amazingly detailed 50 degree orb in this eyepiece. Eye relief is such that I can see the entire fov while wearing glasses.

Planetary eyepieces are great and relatively inexpensive but are optimised for minimum light scattering to provide the best contrast for viewing plannets. This is usally achieved by using the fewest air/glass interfaces at the expense of afovs and eye relief. Depending on the specific eyepiece, and your use and preferences, they may or may not be the best choice.
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Old Thursday 14th December 2006, 22:31   #13
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Thanks Steve. I know you use this test pattern so you know that when looking at astigmatic vertical and horizontal bars at the edge it's difficult to decide when you see the best focus with the least astigmatism. So my figures should be read as no more than rough approximations, + or - one element at best. The center sharpness of all of these eyepieces is excellent. None of them limited visible detail in the center at any magnification for my eyes.

Henry
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Old Thursday 14th December 2006, 22:47   #14
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Yes ,hard to tell best focus.I have to walk away for a while.I can really appreciate your efforts here and to post them so fast.Thanks for the reply to my question.Sounds like there are no real losers here as far as eyepieces go,also sounds like the Hyperion Zoom is a very good buy.
Regards,Steve
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Old Thursday 14th December 2006, 23:50   #15
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Quote:
Originally Posted by greg g
.... On a previous thread I seem to recall it was mentioned that the power of an eyepiece (92x) should not exceed the size of the scope (80x), your Astro-Physics is a 92x. I don't know if this is true, what do you think of that?
If that is true should I then consider a 6mm Burgess Optical/TMB Planetary for a 80x scope? Is that what you meant about "if it will reach focus"?
The famous telescope maker Jean Texereau says that the "best" magnification for detecting small low contrast planetary details (comparable to small low contrast plumage details on a distant bird?) is 20% above a telescope's aperture in millimeters. More magnification causes too much loss of contrast and less magnification doesn't make the details large enough. For an 80mm telescope that would be 96X, but the scope has to be really good for that to be true. Many if not most birding scopes probably do run out of detail and contrast at a lower figure. Maybe you could order or borrow both focal lengths and return the one that you don't like.

I agree with Lou that you should avoid eyepieces with short ER and narrow fields, but the BO/TMB Planetaries are actually pretty good in those categories. The 5mm has 16mm ER and a very well corrected 60 degree field. I think they'd be taken more seriously if the price were raised to $300

If an eyepiece can't reach focus in a particular scope that means it will only focus at close distances. The focuser doesn't have enough travel to bring it to focus at long distances. You'll probably find that not all 1.25" eyepieces will be focusable in your Swaro.

Henry
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Old Friday 15th December 2006, 00:40   #16
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Henry,

Thank you for the guideline of 20% above a telescopes aperture in mm. This means the 5mm Burgess Optical Planetary is in the range! (As you mention you could pucsh to 96x). This is such exciting information. The eye-relief, FOV and Contrast I realize are important. Thanks again for the progressive presentation of information.
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Old Friday 15th December 2006, 00:45   #17
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Lou,
Thanks for the information that the the larger eyepiece works. I will have to check into the Meade 5000 4.7mm. Also thanks for adding that you can see the entire FOV wearing eyeglasses. I wish more people would add that if they experience it. Your description is what I want to have an opportunity to enjoy.
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Old Sunday 17th December 2006, 18:38   #18
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Henry and all,

I did some further checks on the Nikon zoom. The MC II also shows pincushion at all focal lengths. I cannot say if there is more or less than in the MC. I would not consider it excessive, but it was more obvious than the very mild barrel distortion in another zoom eyepiece I was comparing it to (not one of those in your test).

Another thing I ended up testing was how well the eyepiece holds its focus throughout the zoom range. Here, although I knew from experience that the MC II does very well, I was nevertheless surprised to see the result. When focused to best focus at either extreme (7mm or 21mm) with an artificial star and a booster, I could go through the entire zoom range without getting any additional rings to the diffraction pattern. Meanwhile, the other zoom when optimally focused at the shortest focal length would show four rings at the longest focal lengt. I would thus consider the Nikon MC II a true zoom, not an altogether common achievement.

Kimmo
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Old Monday 18th December 2006, 15:00   #19
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I have been able to try the Baader zoom on a Zeiss 85mm Diascope, Swarovski ATS-65HD and Nikon 60mm FIeldscope EDIII.

First the bad news. The Baader will not reach focus on the Nikon beyond about 25m, so an adapter would be useless. We're still at the mercy of Nikon to give us a zoom with a wider field and longer ER.

The Baader will reach focus on the Swaro. It works fine, but the only real advantage it offers over the Swaro zoom is wider field at low magnifications and lower cost (partly offset by the need for a 1.25" adapter). It's not waterproof like the Swaro zoom and doesn't attach as securely to the scope body.

The Baader does attach quite securely to the Diascope by means of a threaded collette that screws onto a set of threads on the scope body that you will see if you remove the eyepiece. Rotating the collette pulls the Baader eyepiece up quite tightly to the scope, but it's not waterproof like the Zeiss zoom attached by the normal bayonet mount. This particular Diascope was not a very good specimen. It had quite a lot of spherical aberration, probably worse than 1/2 wave, so the true performance of any good eyepiece would be invisible through it even at low magnification. The image through the Baader compared to the Zeiss zoom would be a little brighter and a bit less yellow, although a slight yellow color cast is still visible even with the more color neutral Baader in place. I didn't try to compare the eyepieces closely. It seemed pointless to compare one bad image to another, when I know both eyepieces are capable of much better performance.

Last edited by henry link : Monday 18th December 2006 at 15:17.
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Old Saturday 30th December 2006, 15:56   #20
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Henry, this zoom looks really interesting for birders on a budget.

Have you had a chance to see if it would work on the 80mm Pentax PF scopes?
Einaltman has posted it won't work on the 65mm pentax scopes, but it might work on the 80mm models.

Otherwise apart from the Diascopes I wonder what birding scope it could be usefully used on?
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Old Saturday 30th December 2006, 17:10   #21
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I haven't had a chance to try it on the 80mm Pentax. The importer only mentions Zeiss Diascopes and Chinese spotting scopes made by Synta and sold under the Celestron brand name. The Synta scopes are probably sold under other brand names as well. The threads on the eyepiece collette may be the Zeiss 44mm standard that they used on their old astronomical scopes. An adapter ring fits into the collette. It has about 35mm threads which the 1.25" etepiece barrel screws into. Baader could easily make adapter rings to fit other scopes as long as the eyepiece can reach focus. I have found that the Zeiss 2" Diascope eyepiece adapter will fit the Baader collette, but that's no help on birding scopes.
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Old Sunday 4th February 2007, 14:43   #22
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So I'm now wondering if this zoom could work on a Kowa 82mm series scope via a custom made adapter.

The first question would be if it reached focus at infinity assuming there's enough room to mate the zoom to the kowa body.

It doesn't work on the Pentax 80 after all (see Pentax forum).
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Old Sunday 4th February 2007, 15:22   #23
henry link
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I'm also wondering whether the Baader could be adapted to the new Kowa scopes. It would provide a wider field, a litte more magnification (21x-63x) and be much cheaper than the Kowa zoom eyepiece.
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Old Sunday 25th February 2007, 21:52   #24
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Henry,
You had previously mentioned that;
"I agree with Lou that you should avoid eyepieces with short ER and narrow fields, but the BO/TMB Planetary is actually pretty good in those categories. The 5mm has 16mm ER and a very well corrected 60 degree field."
I want to push the envelope when perfect conditions will allow it. I’m considering the 4mm BO/TMB Planetary with 60* FOV and 16mm ER with 5 elements or the 3.6mm Tak has 42* FOV and 6mm ER with 6/3 elements. During consideration of these two eyepieces I was reading about contrast and simple eyepiece construction that allows in more light. The read went into raves for the 4mm AP/SPL and the 4mm TMB supermono for contrast and brightness. The AP/SPL has a 42* FOV, 8mm ER and 3/2 elements while the TMB has 30* FOV with 3.4 ER and 3 elements. Have you had any opportunity to bird watch with these eyepieces or ones with similar specs? I see that you suggest staying away form eyepieces with short ER and narrow fields (I have no experience with eyepieces with this design), the high evaluations because of contrast and light on these eyepieces begs the question, yet there are never any evaluations when it comes to viewing stationary wildlife like a lone bird of prey. Any thought by you or anyone else that has used the above or similar eyepieces would be appreciated.
Greg
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Old Monday 26th February 2007, 23:25   #25
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I have the 4mm TMB SuperMono. IMO it would be a terrible choice for birding. It's a unique monoblock design that sacrifices everthing (FOV, eye relief, off-axis sharpness) to render a very tiny field as bright and contrasty as possible. No problem if you are looking at something that only takes up a degree or two of apparent field like Jupiter through a telescope with a motor drive to keep it centered, but impossible for birding. Besides I don't think the SuperMonos or the AP SPL's are still available. A 5mm eyepiece will be pushing the envelope plenty with your scope. I think more magnification will show no extra detail at all . FWIW I can see just as much in daylight with the 5mm BO/TMB as I can with the slightly brighter 5mm TMB SuperMono.
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